Distinct Sources of Supplementary Protein in the Resistance Exercise Training-induced Adaptations

This is a randomized controlled trial aimed to investigate the effects of different supplementary protein sources on muscle adaptations to resistance exercise. Young, healthy, recreationally active participants consuming an omnivorous diet with protein intake within recommended dietary allowance (RDA) (i.e.; 0.8-1.0 g.kg-1. d-1) will be recruited to undergo a 12-wk supervised resistance training program in combination with the intake of three 15-g daily doses (45g. d-1 total) of either a mixed plant- (i.e.; soy and pea protein) or animal-based (i.e.; whey protein) protein in drink form as a supplementary source of protein to their main meals of the day (i.e.; breakfast, lunch, and dinner). Before (PRE) and after (POST) the 12-wk intervention, participants will be assessed for body composition by dual-energy X-ray absorptiometry (DXA), muscle cross-sectional area (ultrasound) and fiber cross-sectional area (muscle biopsy), and maximal isotonic strength (1RM). Training consists of a resistance training (RT) program individually supervised by a researcher blinded to treatment in a laboratorial setting. Assessments will also be conducted in a blinded fashion.

Inclusion Criteria:Physically active (according to the International Physical Activity Questionnaire (IPAQ)Absence of any chronic condition that could preclude participation in a RT program or physical testingHabitual protein consumption within RDA ≥ 0.8 ≤1.0 g.kg-1. d-1Exclusion Criteria:Prior history of anabolic steroids use, current or previous (≤ 3 m)Use of ergogenic or protein-based supplements, current or previous (< 1 y)Engagement in energy-restricted diets